A fuel battery is a power generation system which oxidizes a fuel by an electrochemical process to directly convert energy discharged owing to an oxidizing reaction into electric energy. The fuel battery comprises a membrane electrode assembly in which both side surfaces of a polymer electrolyte membrane for selectively transporting hydrogen ions are held by a pair of electrodes made of a porous material. Each of the pair of electrodes contains, as a main component, carbon powder which carries a platinum based metal catalyst, and comprises a catalyst layer which comes in contact with the polymer electrolyte membrane, and a gas diffusion layer formed on the surface of the catalyst layer and having both air permeability and electron conductivity.
In this type of fuel battery, in a state where an electrode potential is kept to be high (especially during a low density current operation, an idle operation or the like), the platinum catalyst included in the catalyst layer of the membrane electrode assembly might be ionized and eluted, thereby lowering performance. There is known a method (hereinafter referred to as high potential avoidance control) in which to avoid such a disadvantage, the operation is controlled while limiting the output voltage of the fuel battery to a use upper limit voltage (hereinafter referred to as the high potential avoidance voltage) which is lower than the open end voltage of the fuel battery as disclosed in Japanese Patent Application Laid-Open No. 2005-100820.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-100820